apparmor: reset pos on failure to unpack for various functions

Each function that manipulates the aa_ext struct should reset it's "pos"
member on failure. This ensures that, on failure, no changes are made to
the state of the aa_ext struct.

There are paths were elements are optional and the error path is
used to indicate the optional element is not present. This means
instead of just aborting on error the unpack stream can become
unsynchronized on optional elements, if using one of the affected
functions.

Cc: stable@vger.kernel.org
Fixes: 736ec752 ("AppArmor: policy routines for loading and unpacking policy")
Signed-off-by: Mike Salvatore <mike.salvatore@canonical.com>
Signed-off-by: John Johansen <john.johansen@canonical.com>

security/apparmor/policy_unpack.c

@@ -219,16 +219,21 @@ static void *kvmemdup(const void *src, size_t len)
 static size_t unpack_u16_chunk(struct aa_ext *e, char **chunk)
 {
 	size_t size = 0;
+	void *pos = e->pos;
 
 	if (!inbounds(e, sizeof(u16)))
-		return 0;
+		goto fail;
 	size = le16_to_cpu(get_unaligned((__le16 *) e->pos));
 	e->pos += sizeof(__le16);
 	if (!inbounds(e, size))
-		return 0;
+		goto fail;
 	*chunk = e->pos;
 	e->pos += size;
 	return size;
+
+fail:
+	e->pos = pos;
+	return 0;
 }
 
 /* unpack control byte */
@@ -290,62 +295,84 @@ static bool unpack_nameX(struct aa_ext *e, enum aa_code code, const char *name)
 
 static bool unpack_u8(struct aa_ext *e, u8 *data, const char *name)
 {
+	void *pos = e->pos;
+
 	if (unpack_nameX(e, AA_U8, name)) {
 		if (!inbounds(e, sizeof(u8)))
-			return 0;
+			goto fail;
 		if (data)
 			*data = get_unaligned((u8 *)e->pos);
 		e->pos += sizeof(u8);
 		return 1;
 	}
+
+fail:
+	e->pos = pos;
 	return 0;
 }
 
 static bool unpack_u32(struct aa_ext *e, u32 *data, const char *name)
 {
+	void *pos = e->pos;
+
 	if (unpack_nameX(e, AA_U32, name)) {
 		if (!inbounds(e, sizeof(u32)))
-			return 0;
+			goto fail;
 		if (data)
 			*data = le32_to_cpu(get_unaligned((__le32 *) e->pos));
 		e->pos += sizeof(u32);
 		return 1;
 	}
+
+fail:
+	e->pos = pos;
 	return 0;
 }
 
 static bool unpack_u64(struct aa_ext *e, u64 *data, const char *name)
 {
+	void *pos = e->pos;
+
 	if (unpack_nameX(e, AA_U64, name)) {
 		if (!inbounds(e, sizeof(u64)))
-			return 0;
+			goto fail;
 		if (data)
 			*data = le64_to_cpu(get_unaligned((__le64 *) e->pos));
 		e->pos += sizeof(u64);
 		return 1;
 	}
+
+fail:
+	e->pos = pos;
 	return 0;
 }
 
 static size_t unpack_array(struct aa_ext *e, const char *name)
 {
+	void *pos = e->pos;
+
 	if (unpack_nameX(e, AA_ARRAY, name)) {
 		int size;
 		if (!inbounds(e, sizeof(u16)))
-			return 0;
+			goto fail;
 		size = (int)le16_to_cpu(get_unaligned((__le16 *) e->pos));
 		e->pos += sizeof(u16);
 		return size;
 	}
+
+fail:
+	e->pos = pos;
 	return 0;
 }
 
 static size_t unpack_blob(struct aa_ext *e, char **blob, const char *name)
 {
+	void *pos = e->pos;
+
 	if (unpack_nameX(e, AA_BLOB, name)) {
 		u32 size;
 		if (!inbounds(e, sizeof(u32)))
-			return 0;
+			goto fail;
 		size = le32_to_cpu(get_unaligned((__le32 *) e->pos));
 		e->pos += sizeof(u32);
 		if (inbounds(e, (size_t) size)) {
@@ -354,6 +381,9 @@ static size_t unpack_blob(struct aa_ext *e, char **blob, const char *name)
 			return size;
 		}
 	}
+
+fail:
+	e->pos = pos;
 	return 0;
 }
 
@@ -370,9 +400,10 @@ static int unpack_str(struct aa_ext *e, const char **string, const char *name)
 			if (src_str[size - 1] != 0)
 				goto fail;
 			*string = src_str;
+
+			return size;
 		}
 	}
-	return size;
 
 fail:
 	e->pos = pos;